Hazardous waste handling, transportation and disposal are heavily regulated activities. In particular, hazardous waste must be processed for disposal prior to shipment to the disposal site. Therefore, there is a need for processing methods to enable waste to meet disposal requirements prior to shipment.
There are currently many types of treatment processes for stabilizing hazardous waste including micro-encapsulation, macro-encapsulation, and heat-activation processes. In addition to the effectiveness of the stabilization processes, handling requirements and costs also have an impact on the type of treatment process selected by the waste generator. As requirements and costs increase, generators demand more effective and cost efficient means of waste treatment.
Hazardous wastes may be in the form of sludge, debris, wastes with high organic content, wastes with high nitrate or nitrogen containing content, wastes with high heavy metal content, radioactive wastes, asbestos, liquid solutions and slurries or solids.
One means by which hazardous waste is presently stabilized is through the use of cement. Cement and waste are mixed at ambient temperatures. Hydration and crystallization reactions occur upon the addition of water. These reactions lead to the formation of a monolithic solid in which the waste is chemically bound or encapsulated in the resulting matrix.
Still another treatment process is encapsulation. In encapsulation, polymeric reagents and waste are mixed. Heat is then applied to the mixture to melt the polymer reagent. As the mixture cools, thermosetting polymer reagents such as siloxane, sol-gel, and polyester form long-chain polymers that encapsulate waste in a monolithic solid. Alternatively, thermoplastic reagents such as polyethylene, paraffin, and bitumen may be used.
Heat activated vitrification, another stabilization process, uses glass to form a matrix for encapsulating the wastes. Glass frit or glass forming chemicals are combined with waste and melted to form a fluid mixture that solidifies upon cooling into an amorphous solid. The solidified, stabilized matrix is suitable for transportation and disposal.
Hydroceramic cement stabilization is yet another stabilization process, commonly used on hazardous nitrate waste. This process combines calcine compounds with reagents such as clay, sodium hydroxide, and vermiculite to form a hydroceramnic mixture. The hydroceramic mixture is then mixed with nitrate-containing wastes to form a waste mixture. The waste mixture is heated to activate it. However, this process is limited in the proportion of nitrates that can be input. For example, the maximum nitrate level that can be efficiently immobilized is about 25% of the amount of the alkali metals present. If the amount of nitrates exceeds this alkali metal ratio, some of the nitrate will not be immobilized and can be readily leached from the solid matrix. Furthermore, heat activation temperatures must be kept below about 150° C. to prevent decomposition of nitrates present in the waste.
Yet another heat activation treatment method involves premixing waste materials with additives. The resulting mixture is dried and sintered to achieve the final monolithic waste form. Sintering involves heating the waste and additives to a high enough temperature to partially melt or fuse the waste and additives into a monolithic solid. This method uses three separate operations in three separate process containers.
There is a need for a process for stabilizing hazardous wastes that is more effective and efficient for stabilizing wastes prior to transport, storage and disposal.